Question

which best describes the formation of a zygote?
a sperm cell carrying 46 chromosomes fertilizes an egg cell with 46 chromosomes.
a sperm cell carrying 23 chromosomes fertilizes an egg cell with 46 chromosomes.
a sperm cell carrying 46 chromosomes fertilizes an egg cell with 23 chromosomes.
a sperm cell carrying 23 chromosomes fertilizes an egg cell with 23 chromosomes.

Explanation:

In humans, gametes (sperm and egg cells) are haploid, meaning they have 23 chromosomes each. When a sperm (with 23 chromosomes) fertilizes an egg (with 23 chromosomes), the resulting zygote is diploid with 46 chromosomes. Let's analyze each option:

• First option: Sperm and egg with 46 chromosomes is incorrect, as gametes are haploid (23 chromosomes).
• Second option: Egg with 46 chromosomes is wrong; egg is haploid (23).
• Third option: Sperm with 46 and egg with 23 is incorrect, both gametes should be haploid (23).
• Fourth option: Sperm (23) fertilizing egg (23) is correct, as this forms a zygote with 46 chromosomes (23 + 23).

Answer:

D. A sperm cell carrying 23 chromosomes fertilizes an egg cell with 23 chromosomes. (Note: Assuming the options are labeled A, B, C, D in order as presented, the last option is the correct one with the described content.)